The global shipping industry faces huge pressure to reduce its greenhouse (GHG) emissions due to the International Maritime Organization (IMO) has introduced strict regulations to decrease GHG emissions from ships. New energy sources can provide a solution for green shipping because they have the advantages of abundant, renewable and clean. This paper examines the current progress made regarding the integration of new energy source. The global shipping industry faces huge pressure to reduce its greenhouse (GHG) emissions due to the International Maritime Organization (IMO) has introduced strict regulations to decrease GHG emissions from ships. New energy sources can provide a solution for green shipping because they have the advantages of abundant, renewable and clean. This paper examines the current progress made regarding the integration of new energy sources into conventional ship power systems, including solar energy, wind energy and fuel cells. It also discusses the possibilities for using the aforementioned three new energy sources in ship power systems ranging from technical principles to subsequent applications. Furthermore, basic working theories of new energy sources, application methods, existing new energy ships and core technologies required are summarized in detail. The integration of new energy sources into traditional ship power systems has enormous potential to bring the shipping industry in line with international regulatory requirements and is set to become a key focus of ship-related researches in the immediate future.••New energyShip power systemShip microgridCritical technologyShipping now is one of the most critical modes of transportation for world trade, accounts for approximately 90% of global trade [1,2]. However, the shipping industry has also become one of the main contributors to global GHG emissions, currently responsible for about 3% of the global total [3,4]. According to an evaluation carried out by the Intergovernmental Panel on Climate Change (IPCC), if global output of GHG emissions can be reduced by 40%–70% before the year 2050, the rise in the temperature of the earth surface can be limited to under 2 °C, otherwise the temperature will rise by 3 °C–5 °C. In addition, ships almost inevitably emit sulfur oxides (SOx), nitrogen oxides (NOx) and particulate matters (PM), which are also contributors to air pollution. So, the IMO has introduced strict regulations such as the Energy Efficiency Design Index (EEDI) and the Ship Energy Efficiency Management Plan (SEEMP) to try and lower the level of GHG emissions from conventional ships [,, ]. Furthermore, some emission control areas (ECAs) in North America and Northern Europe have been set up to limit the SOx and NOx emissions from ships. Overall, the shipping industry is confronted with an urgent need to move away from its current near-total reliance on fossil fuels.Those strict regulations combined with ecological consequences of massive GHG emissions have prompted technical experts to explore energy-saving an. Since fossil fuel reserves are limited and environmental issues are becoming more serious, governments and researchers have paid more and more attention to the use of new energy sources, such as solar energy, wind energy, fuel cells, hydro energy, biomass, geothermal and ocean energy [17,18]. Solar energy, wind energy and ocean energy are intermitt. Solar energy, wind energy and fuel cells are used first to generate electricity, which can be then used by a ship's power system. After introducing new energy sources into ships, the related issues include system stability, grid reliability and power quality emerged because of their intermittent nature. Microgrids offer a promising solution here [86,87]. As an important feature of notional 'smart grids', microgrids have been adopted in terrestrial new energy generation systems. A microgrid (Fig. 8) is defined as a small distributed system that consists of a series of micro-sources, including PV arrays, wind turbines, energy storage systems, controllable and uncontrollable loads [,, ]. A switch needs to be installed at the point of common coupling (PCC) between the microgrid and the public grid to change the microgrid operation mode from grid-connected mode to stand-alone mode. In grid-connected mode, the microgrid can receive/deliver electricity from/to the main grid via the PCC.To maintain the stability of the microgrid voltage and frequency by using different control strategies to regulate the output power of the distributed generation systems according to the power demand of the load is a core feature of control techniques [,, ]. Other than control strategies, quite a lot of related studies have been done in microgrids optimization [94,95], configurations and applications, operating control and protection devi.
